To increase the response speed of liquid crystal, a method called overshoot driving or overdrive driving has been used. Japanese Patent publication Tokukosho 63-25556/1988 (published on May 25, 1988) discloses an example of such a method.
The method realizes an increase of the response speed by providing extra change to a liquid crystal module that has been changed by the input data. The following more specifically explains this technique.
For example, now assumes a liquid crystal module capable of 256 gradations.
Then, also assume that a picture element of the liquid crystal is displayed as gradation 0, and then changes to gradation 64 in response to the next input signal. In this case, it may occur that the liquid crystal responses so slowly to application of a voltage corresponding to 64 gradation that the gradation level does not reach 64. Similarly, further assume that the picture element is supplied with a voltage corresponding to gradation 84 but the liquid crystal responses so slowly that the gradation level does not reach 80 but reaches only 64.
Under such a condition, the liquid crystal is controlled to be changed from 0 to 80, instead of controlling it to be changed 0 to 64, so that the gradation reaches 64 more quickly. This is the method called overshoot driving or overdrive driving, that has been used for liquid crystal TVs of various manufacturers since when the duration of the patent of the foregoing publication had run out.
However, the conventional liquid crystal display device has a problem as follows.
In recent years, a liquid crystal display device, that had conventionally been used as a display device for a computer, is more often used as a display device for displaying a moving picture. This application has become more common with the development of a liquid crystal display device for a TV, and improvement of performance of a computer that is now capable of displaying a moving picture.
However, a critical problem of a liquid crystal module in use for a display device of the moving picture is low response speed of a liquid crystal. Namely, displaying a moving picture by a liquid crystal display device with a low response speed causes image-lag, thereby decreasing display quality. The response speed of the liquid crystal display device is particularly slow in a change between a halftone to a halftone compared to a change in monochrome display. Therefore, the degradation of display quality becomes significant in a particular moving picture of live action.